In some applications, including underwater transmission links, it is necessary to provide optical fiber cables which are not only sealed, but which also resist longitudinal propagation of water after water has infiltrated the cable via a damaged portion thereof. Such resistance to longitudinal water propagation is obtained by filling the channels in which the fibers are loosely disposed with a hydrophobic viscous material, and is only effective after a certain length of intact cable.
At the points at which the cable enters repeaters, this technique is inappropriate since there is no guarantee that there will always be a sufficient length of intact cable. One known way of solving this problem is described in French patent application No. 2 435 845 (equivalent to British specification No. 2 030 011 and U.S. Pat. No. 4 262 913) and consists in using a tube through which the bundle of optical fibers in the cable passes at the feed-through in the sealed wall of a repeater housing, this tube is filled with a block of plastic coating material which adheres both to the fibers of the bundle and to the inside wall of the tube, with the tube being fixed in sealed manner through the wall of the repeater housing.
The sealing device obtained in this way suffers from the danger of leaks arising in the long term along the inside wall of the tube since the plastic coating material tends, over a long period of time to shrink somewhat.
Another longitudinal sealing device is known which avoids this drawback and in which the walls of the optical fibers are coated and then embedded in a metal cone insert constituting the central part of a seal. However, this device suffers from the drawback of being difficult to implement without making the optical fibers more brittle.
The aim of the present invention is to mitigate these drawbacks.